Patients who have had strokes and are taking Lipitor (atorvastatin) to lower their cholesterol may be at increased risk of a brain hemorrhage, a new study finds.

However, researchers caution that the medication's value — its prevention of ischemic strokes — needs to be weighed against the risk.

A brain hemorrhage, or hemorrhagic stroke, involves the rupture of weakened blood vessels in the brain, leading to rapid bleeding. An ischemic stroke is caused by an obstruction within a blood vessel supplying blood to the brain.

"The risk of hemorrhage in patients who have had a transient ischemic attack or stroke must be balanced against the benefits of cholesterol-lowering drugs in reducing the overall risk of a second stroke, as well as other cardiovascular events," said study author Larry Goldstein, with Duke University Medical Center in Durham, N.C., in a release.

The study was a secondary analysis of a double-blind, randomized clinical trial funded by Pfizer, the company that makes Lipitor.

Participants were enrolled between September 1998 and March 2001and followed for an average of 4.5 years.

Researchers found that 2.3 per cent of 4,731 patients who had suffered a stroke in the previous one to six months experienced a brain hemorrhage during the study period, compared to 1.3 per cent taking placebo. They were taking 80 mg of Lipitor each day

But taking Lipitor also reduced patient's risk of fatal and non-fatal ischemic stroke by 21 per cent, as well as leading to a significant decrease in "coronary events."

According to the study, people who were more likely to experience a hemorrhage included those who'd had one before beginning treatment with the anti-cholesterol drug, older people, men, and people with untreated high blood pressure.

Levels of LDL or total cholesterol, smoking status or use of anti-platelet drugs or blood-thinning medications did not affect the risk of stroke, researchers found.

The study is published in the Dec. 12 online edition of Neurology, the journal of the American Academy of Neurology.